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Bulletin of Environment, Pharmacology and Life Sciences Bull. Env. Pharmacol. Life Sci., Vol 3 (2) January 2014: 113-120 ©2014 Academy for Environment and Life Sciences, India Online ISSN 2277-1808 Journal’s URL:http://www.bepls.com CODEN: BEPLAD Global Impact Factor 0.533 Universal Impact Factor 0.9804

ORIGINAL ARTICLE

Chemical Composition of Fumarolic Gases and Springs Discharges from the Taftan volcano; with Emphasis on the Geochemical Behaviour of Arsenic

Zahra mokhtari1*, Ali Ahmadi1, Marziyeh Hosseininasab 1: Department of Earth Sciences, Faculty of Sciences, University of Sistan and Baluchestan, Zahedan, Iran. 2: Department of Mining Engineering, Faculty of Engineering, University of Sistan and Baluchestan, Zahedan, Iran E-mail:[email protected]

ABSTRACT Taftan volcano located in SE Iran, releases significant volcanic gas during current fumarolic activities; while a few magmatism-related springs occur all around the volcano. Spring waters are genetically related to the fumarolic gases. Sulfur is the common element in fumarolic gases; its concentration is 860 mg/L in one analyzed sample. Water-gas interactions are caused higher temperature and lower pH in waters, and facilitate water-rock interaction. All of this processes cause high concentrations of elements such as S, Al, Fe, Ca, Na, K, and Mg in this waters. Taftan magmatic gases and waters contain arsenic in the range from less than 0.005 to 1.72 mg/L. Arsenic concentration correlates negatively with pH values. Eh-pH diagram indicates that As (III), the most hazardous type, is the common species in the Taftan magmatism-related waters. Keywords: Taftan, volcanic gases, thermal and mineral springs, arsenic.

INTRODUCTION Thermal and mineral springs are generally found in regions of young volcanic activity as a result of eruptive events, as well as obvious manifestations of long-lived hydrothermal systems. Surface water percolates downward through the rocks below the Earth's surface to high-temperature regions surrounding a magma reservoir, either active or recently solidified but still hot. As the water heats, the density gets low and rises back to the surface along fissures and cracks. The temperature and rate of discharge of thermal springs in various volcanoes or even in a single volcano is different. These two parameters are dependent on several factors such as the water circulation rate through the system of underground channel ways, the amount of heat supplied at depth, and the extent of dilution of the heated water by cold ground water near the surface. Thermal springs are frequently developed as spas and bathing facilities, improving social and economic well-being. Other useful applications of these springs in volcanic regions are related to direct application of heat production for domestic uses, greenhouse heat supply and power production, which depend on the discharge volume and temperature, or to geo thermal resources investigation [22]. The geochemistry of thermal waters is a useful tool for volcanic activity monitoring [e.g. 14, 19] and numerous studies have been conducted in active volcanic regions worldwide [9, 18, 20, 15]. Late Cenozoic; especially quaternary; is the time of tremendous volcanic activity on Iran. Several large volcanoes have been formed during this period. The most important volcanic centres are Damavand (N of Iran), Sahand and sabalan (NW of Iran), Taftan and Bazman volcanoes (SE of Iran). All of them are more or less extinct, and in spite of well-preserved morphology only a few are still in active post-volcanic stage. Among them Taftan and Damavand volcanoes have attracted particular interests. Volcanic activity in both of them is limited to emission of fumarolic gases, solfatars and some hot springs. Apparently, this has been the case for the last few thousand years. Anyway fumarolic activities are stronger in Taftan compared to Damavand.

Several surveys are already carried out in the Taftan volcano [8, 3, and 2]. The studies mainly deal with geological, petrological, environmental, geochemical, and hydrothermal and hydrogeological aspects of the area. However, there is no published data on gas chemistry and arsenic behavior in thermal and mineral springs of Taftan. In environmental studies at volcanic region, the chemical compositions of volcanic gases and vapours are such important. Arsenic is one of the most important elements that can be added to the environment as a result of volcanic activity; It has been identified as a public health problem because of its serious toxic effects even at low exposure levels and is widespread in the environment [10, 17]. The present study is aimed at defining the chemistry of volcanic exhalation and hot and cold springs of the Taftan volcano and determining the arsenic species in the thermal waters. The final results are useful to plan further development with the environmental approach on the southern flank of Mount Taftan and in the other active volcanic areas in the world, as well. Geological features of the Taftan Volcano Large volcanic centers including Taftan, Bazman and koh-i-Soltan (in Pakistan) are located in the active Makran volcanic belt; these volcanoes represent those which were formed by subduction of the Oman oceanic lithosphere underneath the continental Eurasia plate [5]. Tftan volcano is located between 28030ʹ - 28030ʹ northern and 61000ʹ - 61015ʹ eastern, 100 km to the south-southeast of zahedan and 45 km to the north of khash (SE Iran) (Fig. 1). Taftan area is, on average, 1500 m higher than surrounding terrains, while the summit of the volcano is at 4350 m above sea level. The volcano consists mainly of two prominent summits, Narkuh and Matherkuh, together with a thin saddle horse-like part. The S. Matherkuh (youngest summit of Taftan) which is covered with thick and young andesite lava flows, showing highly sulfur-encrusted fumaroles activity (Fig. 2). The volcanic rocks in Taftan are similar to island-arc, calk-alkaline series and are related to the subduction of the Arabian Plate underneath the Makran region [5]. It is concluded that Taftan magmas have had mostly acid composition and Taftan rocks, whatever their occurrence, belong mainly to the dacite and quartz andesite rock families. In general, volcanic rocks in Taftan are divided into quartz- andesite, dacites, ignimbrite and aquagene tuff. Rocks with andesite and dacites composition also comprise a significant proportion of Taftan volcanic and may occur as lava flows or volcanic plugs. Taftan ignimbrites also have andesite composition. Sporadic and relatively small occurrences of basaltic lava flow have been observed and studied around the Taftan. A simplified geological map of the Taftan area is presented in Fig. 3.

Fig.1. Taftan volcano location in Iran

Fig.2. Post volcanic activity and Sulphur emissions in Taftan volcano

Fig.3. Simplified geological map of the Taftan and surrounding area (scale=1:100000). 1. Alluvial plain; 2. andesite lava flow; 3. dacite and andesite lava flow; 4. andesite and dacite lava flow; 5. andesitic tuff, dacite, ignimbrite, pyroclastic and volcanoclastic; 6. andesite and dacite lava flow and volcanic breccia; 7. pelitic shale and basalt lava flow.

MATERIALS AND METHODS Field work was conducted on the west flank of taftan volcano. We sampled the 1 fumarole gases, and 8 thermal spring and surface stream waters for chemical analysis. Location of sampling areas can be seen on the satellite image of the Taftan region (Fig. 4). Physical and chemical characteristics of the collected water samples in volcanic areas are depended to the time highly. Therefore, to avoid any error in the results, we have to sampling from the inception of springs, or nearest locations to them. The discharge rates of these springs vary from less than 0.5 to 10 L/s and their fluid temperatures range between 6º and 50ºC. Physicochemical parameters of the waters, such as temperature, pH and redox potential (Eh), were measured in the field. All of the samples (gas and thermal & cold mineral water springs) were collected in a polyethylene container with a volume of 70 ml, and after the addition of some nitric acid, completely shut the doors. Each bottle was rinsed three times before being filled. Waters were chemically analyzed in ALS-Chemex laboratory using Inductively Coupled Plasma (ICP) methods.

Fig.4. Location of sampling areas on the satellite image of Taftan area Arsenic geochemistry Arsenic (symbol As) is a semi-metallic element with the atomic number 33 is placed in group VA of the periodic table. Arsenic levels in the Earth's crust are small naturally; it varies at ranges between 0.5 and 2.5 mg kg–1 and distributed in more than 320 minerals [7]. The most common minerals are arsenopyrite (FeAsS) [17], orpiment (As2S3), realgar (As2S2), and solid solution in pyrite (FeS2) [4]. Arsenic is also found in sedimentary environments adsorbed by Fe (III) and Mn (IV) after weathering of sulfide minerals [13]. The complex chemistry of arsenic in the environment is cause of various oxidation state of this element. 3+ 5+ - - Arsenic exists mainly in three valency states (i.e., -3, +3, and +5). As (H3AsO3) and As (H2AsO4 /HAsO4 2) are widely present in natural waters [6] and are soluble over a wide range of pH and Eh conditions. In oxidizing environmental conditions, As5+ species are more stable and predominant, whereas in reducing environmental conditions, As3+ species are predominant [1]. In addition, arsenic is present in solid form, which is not quantitatively important. In solid state, arsenic appears as a silver-gray and brittle that tarnishes in the air. The most common organic states for this element are dimethylarsinic acid (DMAA) and monomethylarsonic acid (MMAA), and trimethylarsine oxide (TMAO). The toxicity of methylated forms is low and the volatile forms are not stable under oxidizing conditions [17]. As (III) (arsenite) is reported to be 25–60 times higher than that of As (V) (arsenate). The toxicity of arsenic decreases in the following order: arsines > arsenites [inorganic As (III)] > arsenoxides [organic As (III)] > arsenates [inorganic As (V)] > arsonium compounds > metallic arsenic [11]. Despite the different degrees of toxicity, there is no distinction between the arsenic species in water quality standards.

RESULTS AND DISCUSSION The chemical composition of exhaust gases and springs of Taftan volcano The results of the chemical analyses of gas and water sample of springs are presented in Table 1. During sampling, the gas temperature has been measured between 70-85 ° C and pH of the distillate product equal to 1.65. As shown in Table 1, Sulfur is the most common element in fumarolic gases of Taftan. Furthermore, the concentration of hazardous environmental elements, such as arsenic, is 0.672 mg/L.

strongly acidic pH indicates the presence of H2SO4 in the gas composition of the Taftan volcano. The presence of this compound in the exhaust gases is evidence of the high oxygen fugacity in the magma chamber of Taftan. On the basis of the result of chemical analysis and pH values, the taftan spring waters can be divided into three groups. The first group is strongly acidic water (pH = 1.7- 2.6) and high concentration of elements. This group includes the symbols of SP1, SP2 and SP4 in Table 1, which occur at higher elevations and near the active crater of Taftan. The second group (Sp3, Sp5 and Sp6 in the table 1) of spring show almost acidic pH (from 4.3 to 5.3) and lower concentration of elements. In both groups, especially in the first, the waters are highly acidic and oxidizing solutions specifically. The main cations in these two groups are included Al, Fe Ca, Mg, Na and K. low pH in these waters is the result of SO4 adsorption and formation of sulphuric acid. According to the table 1, sulphur is the dominant element in these springs compared to other. The proportion of S in these waters depends upon the composition of the original magmatic vapour [9]. High concentration of sulphur is caused through absorption of magmatic vapours by the deep circulating groundwaters. The third group (Sp8 & Sp7 in table 1) consists of waters on the lower flank of Mount Taftan (at about 2200 m elevation). These waters have natural pH from 7.41 to 7.44 and lower concentration of element compared to other groups. The main anion in these springs is HCO3, and like the other two groups; Al, Fe, Ca, Mg, Na and K are more abundant than other elements. Arsenic in volcanic gases and mineral springs of Taftan Arsenic is a potentially toxic contaminant of concern even at relatively low concentrations in the environment [17, 10]. According to WHO, (2001) upper permissible limit of arsenic in potable water is 0.05 mg/L. As mentioned before, arsenic concentration in Taftan volcanic gases is equal to 0.672 mg/L. This amount is more than 13 times more than the lower limit of arsenic in drinking water. Furthermore, the concentration of arsenic in the springs with high sulphur content is also significant. For example, arsenic concentration in Sp1 (hot spring) is 1.72 mg/L. This value is 30 times more than the permitted limit for this element. However, most of the springs in the flanks of Taftan have not drinking usage, but high concentration of this element can be serious threat for drinking water sources in surrounding area. Mineral springs are part of the hydrologic cycle and can transferred contaminants into groundwater. The main origin of arsenic in all springs of region is magmatic. This is indicated by significant concentration of this element in chemical composition of Taftan gases. Moreover, several processes have been invoked to account for high levels of arsenic in natural water from around the world. Several reactions are responsible for the content and mobilization of arsenic in surface waters: 1) reductive dissolution of arsenic-rich iron oxy-hydroxides derived from weathering of sulfide minerals [13]. This process could be responsible for the high concentrations of arsenic in groundwater. In nearly all cases, the large scale of arsenic contamination in groundwater, caused by iron oxide reactions in the aquifer sediments. Reduction of iron oxy-hydroxide (FeOOH) and releasing of its absorbed arsenic load to solution is an important mechanism that groundwater in the worldwide becomes polluted with arsenic [13]. However, on the surface water, this factor has been almost ineffective, because due to oxygen fugacity, optimum conditions for the reduction of these compounds are not easily available [13]. 2) Oxidative dissolution of arsenic-rich pyrite or arsenopyrite [17, 4]. 3) water-rock reaction with other arsenic-bearing minerals [17]. It seems that the high occurrence of arsenic in the springs of Taftan is created by the latter two processes. As a result of high temperature and acidic pH, water solubility power has increased dramatically in some of springs, therefore facilitates water-rock interactions, moreover, oxidative dissolution of arsenic- bearing minerals will be increased. Consequently, as we can see in Table 1, the concentration of arsenic in the hot spring water (SP1) is considerable as compared to others. With decrease in temperature and increase in pH, the concentration of arsenic in spring’s water is reduced gradually and it is less than 0.005 mg/L in SP5. Arsenic in the geochemical cycle In order to solve environmental problems related to arsenic, identification of processes that control its concentration, as well as recognizing different species of arsenic in the natural environment is essential. The Eh (Redox potential) and pH (Acidity) are the most important parameters that control the speciation of As in ground waters [16]. The values of these parameters for all of Taftan springs are presented in Table 1. According to this table, redox potential (Eh) and pH values for all of samples, varies from 358.1 to 385.4 mV and 1.65 to 7.44 respectively. Construction of Eh-pH diagram for arsenic reveals that the As (III), the most hazardous type, is the predominant species in Sp1, Sp2 and Sp4 (Fig. 5). In the other samples, arsenic is present as As (V). In this figure dotted lines indicate the limits of water stability. In general, the ratios of As(III) and As(V), as well as total arsenic concentrations, are controlled by pH, redox conditions of groundwater, adsorption / desorption processes of metal hydroxides, dissolved oxygen

BEPLS Vol 3 [2] January 2014 117 | P a g e ©2014 AELS, INDIA Mokhtari et al value (DO), temperature, alkalinity and the source of arsenic [12]. Figure 6 demonstrates arsenic concentrations vs the content sulfates. As shown in this figure, by reducing the amount of sulphate, arsenic levels are reduced. Furthermore arsenic concentration correlates negatively with pH values.

Fig.5. Distribution of arsenic concentration in Eh–pH diagram.

Fig.6. Relation between total arsenic concentration and sulfate component

Table 1. Chemical and physical data of gas exhalation and Thermal Springs waters of the Taftan (concentrations in mg/L). G.S SP1 SP2 SP3 SP4 SP5 SP6 SP7 SP8 S 860 3410 1700 70.90 3770 167 116 7.05 24.90 0.007 <0.00 0.013 <0.00 0.025 As 0.672 1.72 0.551 0.886 6 5 9 5 2 Ca 9.31 451 345 107 582 193 148 21.9 30.5 K 15 313 314 10 329 20.8 14.2 4.67 4.84 Na 2.49 420 314 32.5 521 66.3 49.2 40.9 40.8 Mg 1.62 186 164 24.2 248 35.7 35.7 4.43 8.02 Al 4.64 1780 1130 0.706 2250 51.60 20.1 0.02 0.018 0.042 Fe 3.20 524 195 0.304 570 0.190 0.435 0.428 6 pH 1.65 1.68 2.63 5.3 2.1 4.31 4.43 7.7 7.44 Eh * 365.3 365.5 361.5 363.6 385.4 362.9 359.4 362.6 T (C0) 80 48 32 7 9 13 13 10 10 *: not measured

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How to cite this article: Zahra M, Ali A, Marziyeh H. Chemical Composition of Fumarolic Gases and Springs Discharges from the Taftan Volcano; with an Emphasis on Geochemical Behaviour of Arsenic. Bull. Env. Pharmacol. Life Sci. 3 (2) 2014: 113-120